[lcrisci]

Bookmark the following url and come back to it as often as you need:

http://tldp.org/LDP/abs/html/

Also this one to learn some cool tricks:

http://www.commandlinefu.com/commands/browse

[lloeki]

Yes for ABSG, especially the manipulating strings and process substitution.

That and shellcheck(+syntastic if you use vim) ramps up the skill level quite fast.